he's also a professor of mechanical engineering at uc davis. >> not all of them are safe. >> reporter: hubbard said the key to preventing serious accidents is calculating the distance from the jump to the landing. >> basically accommodates for anyplace you want to land and makes it so that you land equally softly everywhere. >> reporter: while ski resorts typically keep accident statistics private, a recent study presented at a conference organized by the international society for skiing safety found the rate of spine and head injuries at terrain parks is double that compared to other areas at a resort. >> i had no idea that these jumps really have almost little to no design. >> reporter: when kenny hit a jump at more than 35 miles an hour at a terrain park at the summit in snoqualmie, washington, it sent him more than three stories up in the air. >> it dropped me down on the flat ice instead of dropping me down to a more of a sloped landing, which in theory would have prevented me the injury that i got. >> reporter: paralyzed from the neck down at 23 years old, he received more than